a doubting Thomas
A skeptic. A reference to the New Testament story about the Apostle Thomas, who refused to believe that Jesus had risen from the dead until he saw him in person. Lisa's husband was a real doubting Thomas when she told him she'd won the lottery. He demanded to check the ticket himself.
a doubting Thomasa person who refuses to believe something without having incontrovertible proof; a sceptic.
In the Bible, the apostle Thomas said that he would not believe that Christ had risen from the dead until he had seen and touched his wounds (John 20:24–9).